Process for reducing or avoiding foam production during chemical and physical materials conversion processes and a device for performing this process

ABSTRACT

The production of foam which occurs in many chemical and physical materials conversion processes can be avoided by performing the materials conversion process in an ascending jet reactor, including a baffle-free container with a tapering lower section, preferably a conical lower section, and a device for gas injection, and the contents of the reactor are thoroughly mixed by means of ascending jet circulation caused by gas injection.

INTRODUCTION AND BACKGROUND

The present invention relates to a process for reducing or avoiding foamproduction during chemical and physical materials conversion processesin a liquid medium, wherein the materials conversion is performed in ahopper-shaped reactor with thorough mixing of the contents of thereactor. The invention also relates to a device for performing theprocess.

In many chemical and physical materials conversion processes more orless intensive foam production occurs which makes process controldifficult or even impossible. Thus specific measures are required inorder to break down the foam and/or to avoid the production of foam orat least to reduce it to an acceptable level. Although foam productioncan sometimes be avoided or reduced by managing the flow conditions inthe reactors, for instance by avoiding sharp bends in the flow andlocating liquid inlets below the surface of the liquid, in many casesthese types of action are not enough. Accordingly, processes forbreaking down the foam, including thermal, chemical and mechanicalprocesses, have to be used. A review of this topic is provided by Pahlet al., Chem.-Ing.-Tech. 67 (1995), 300-312. The process engineeringinvolved becomes more complicated when using known measures for breakingdown foams and/or the product purity of the product being produced isreduced by the use of chemical antifoam agents. In addition, theproduction costs are increased.

A variety of reactors have been disclosed for performing batchwise andcontinuous crystallization processes in which foam problems often occurdue to intensive internal or external circulation of the liquid reactionmedium containing the growing crystals. A review of this topic isprovided in Ullmann's Encyclopedia of Industrial Chemistry, 5th ed.(1988) vol. B2, 3-22 to 3-25. For example, a crystallizer with forcedexternal circulation includes an evaporation tank, a circulation systemwith pumps and heat exchanger as well as a feed pipe for the solutionbeing supplied and a withdrawal port for the crystal suspension. Overand above the problems associated with foam production, secondary seedcrystal formation occurs as a result of the mechanical circulationsystem and this leads to the production of a finely divided product,while there is a risk of incrustations forming in the heat exchanger.

Vacuum crystallizers with internal circulation of the crystalsuspension, for example a Swenson or Standard-Messo crystallizer,contain a guide tube located in the tank or a variety of shapes of guidemetal sheeting and an agitator. It has been shown that, even in thesetypes of crystallizers, foam is often produced which then requires theuse of antifoam agents or special devices for breaking down the foam.Here again, the particles are broken down due to the input of mechanicalenergy via the agitator and as a result of deflections on encounteringthe baffles. Although the proportion of fine particles is reduced byreducing the speed of rotation of the agitator, incrustations andproblems due to insufficient mixing then occur. These types of problemshave been observed in practice when preparing sodium perborate inaccordance with the process described in CAV 1973, pages 45-50.

According to classical crystallization theory, although poor particlenumber control in crystallizers of the type mentioned above can beimproved by chemically influencing the production of seed crystals or bythe dissolution of seed crystals or by structural separation of the seedcrystal production and particle growth zones, these types of measuresare associated with additional expense. Although the process accordingto EP-B 0 452 164 makes use of these types of measures during thepreparation of sodium perborate, the foam problem is not solved and,depending on the choice of surface-active substance used in thisprocess, may even be intensified.

The hydrodynamic behavior of a suspension in a reactor with a lowersection which tapers to a point, for example a cylindrical containerwith a conical lower section which is agitated by gas injection by meansof nozzles arranged at a point source or in a line at the tip, has beenstudied many times; see R. H. Kleijntjens et al. in the Canadian J. ofChem. Engineering 72 (1994), 392-404 and Y. T. Shah et al. in Chem. Eng.Comm. 110 (1991), 53-70. In these types of reactors, there is an upwardsdirected flow in the region of the stream of bubbles and, parallel tothis, a downwards directed backflow near the walls. The solidsconcentration is at its highest in the lower region of the conical partof the container. These above documents mentioned do not suggest usingthese types of ascending jet reactors to minimize foam productionoccurring during a materials conversion process or as a crystallizationreactor for continuous crystallization. This type of use, again, is notobvious from the details given in VerfahrenstechnischeBerechnungsmethoden, part 4 (1988), chapter 6, in particular pages158-159, 167-169 and 206-209, since in that document (page 208)reference is made to the foam problem and the use of chemical antifoamagents is recommended for controlling foam.

Accordingly, an object of the invention is aimed at performing chemicaland physical materials conversion processes with substances dissolved ina liquid phase and/or suspended therein, and with thorough mixing of thecontents of the reactor, in such a way that it is possible to performthe process without any significant foam problems.

A further object of the invention is to achieve the above by usingsimple engineering means and avoiding or minimizing the addition ofantifoam agents.

A still further object of the invention is to improve physical materialsconversion processes, and especially a crystallization process, whereina dissolved substance is crystallized out. Chemical materials conversionprocesses may be any chemical reactions, in particular those which areperformed in the presence of a solid suspended in a liquid medium, forexample a solid catalyst, or during which a solid is formed, forinstance by reaction and subsequent crystallization or bypolymerization.

SUMMARY OF THE INVENTION

The above and other objects of the invention are achieved by a processfor reducing or avoiding foam production during chemical and physicalmaterials conversion processes in a liquid medium, wherein the materialsconversion is performed in a hopper-shaped reactor with thorough mixingof the contents of the reactor.

It is a feature of the invention that an ascending jet reactor which issubstantially free of baffles, tapering in the lower section andprovided with a device for gas injection in a position which enablesascending jet circulation, is used as a reactor and thorough mixing ofthe contents of the reactor is achieved by gas injection.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be further understood with reference to the drawings,wherein:

FIG. 1 shows a schematic diagram of a preferred ascending jet reactor,in longitudinal section; and

FIG. 2 shows a specific embodiment of the lower section of a reactor ofthis type, also in longitudinal section.

DETAILED DESCRIPTION OF INVENTION

Any chemical and physical materials conversion processes, in whichperforming intensive, thorough mixing of dissolved and/or suspendedmaterials participating in a materials conversion process in a liquidmedium is required, may be amenable to the process according to theinvention, which may be performed batchwise or continuously. Physicalmaterials conversion processes comprise in particular the conversion ofa dissolved substance into a solid substance, thus crystallizationprocesses, wherein the process according to the invention isparticularly suitable for continuous crystallization. Chemical materialsconversion processes may comprise, for example, the formation of areaction product from two or more reactants or a polymerization process.In these types of processes a solid may be present suspended in theliquid medium, for example a suspension catalyst or a dissolvingreactant, or insoluble reaction products may be formed in the liquidmedium. One of the reaction partners may also be a gaseous substancesupplied to the reactor. The process is particularly suitable for thosereactions in which a solid, which may have a low or a high molecularweight, is formed or in which a suspended catalyst is continuouslyremoved from the reactor and then returned after regeneration.

In carrying out one aspect of the invention, the process calls forreducing or avoiding foam production during chemical and physicalmaterials conversion processes in a liquid medium, by performing thematerials conversion in a hopper-shaped reaction zone with thoroughmixing of the contents of the reaction zone.

The reaction zone is an ascending jet reaction zone which issubstantially free of baffles, tapering in the lower section andprovided with gas injection in a position which enables ascending jetcirculation. The thorough mixing of the reaction contents is achieved bygas injection.

In further detail, the process of this invention is especiallyapplicable for the materials conversion in a crystallization process,wherein a solution of the compound to be crystallized or solutions ofraw materials for the in-situ formation of a solution of the compound tobe crystallized is introduced continuously or periodically to theascending jet reaction zone. In this embodiment the solutions aresupersaturated or the supersaturation is produced by vaporizationcooling, and a solids-rich suspension is withdrawn through a portlocated in the wall of the lower section of the reactor zone.

In the embodiment of the invention where the materials conversion is acatalytic reaction involving the formation of a polymer which isinsoluble in the liquid medium, one or more monomers and catalyst areintroduced to the ascending jet reactor zone and a suspension rich ininsoluble polymer is withdrawn through a port located in the wall of thelower section of the reactor zone.

When carrying out a catalytic reaction in accordance with the inventionwherein the materials conversion is a catalytic reaction in the presenceof a suspension catalyst which has to be continuously regenerated, oneor more of the solutions containing compounds to be reacted can beintroduced to the ascending jet reactor zone continuously orperiodically. A phase rich in suspension catalyst is then withdrawnthrough a port located in the walls of the lower section of the reactorzone and the catalyst is returned to the reactor zone afterregeneration.

According to a specific embodiment of the invention the materialsconversion can be the preparation of a hydrogen peroxide reactionproduct selected from the group consisting of sodium perborate, sodiumpercarbonate and form amidine sulphinic acid. In this aspect of theinvention an aqueous hydrogen peroxide solution and a solutioncontaining a substance selected from the group consisting of sodiummetaborate, sodium carbonate and thiourea is introduced to the ascendingjet reactor zone filled with a saturated solution of the H₂O₂ reactionproduct be prepared. The ratio of components is at least in accordancewith the stoichiometric requirements. A solids-rich suspension is thenwithdrawn through a port located in the wall of the lower section of thereactor zone.

The liquid medium generally employed according to the invention is asolution in water, an aqueous/organic solvent or a purely organicsolvent. Due to the gas injection procedure and thus the fact that thegas becomes loaded with solvent vapor, and optionally the requirement torecover this, sufficiently high-boiling organic solvent systems or suchsolvent-containing aqueous/organic systems or water are substantiallyused, wherein water is particularly preferred.

The materials conversion process may take place at any suitabletemperature. Temperatures of about −10° C. to 150° C. are generallypreferred. If water is used as the solvent in the liquid medium, thetemperature is expediently between the freezing point and 100° C. Thepressure during materials conversion may also vary over wide limits,being below, at or above atmospheric pressure. When using a reactordesigned as a vacuum container, materials conversions may be performedunder reduced pressure, for instance under the conditions ofvaporization cooling.

A device for performing the process according to the invention has alsobeen found, this comprising an ascending jet reactor which consists of acontainer which tapers over the lower section with a device for gasinjection in a position which enables ascending jet circulation, whereinthe reactor contains a port in the tapering lower section forwithdrawing a solids-rich suspension and, above the device for gasinjection, an inlet pipe for introducing a liquid medium, wherein thedischarge opening in the inlet pipe is located in the region of thestream of bubbles being produced when the container is in the operatingstate.

The reactor to be used is designed as an ascending jet reactor whichenables extensive circulation of the contents of the reactor by means ofpoint source or linear gas injection. In order to produce undisturbedextensive circulation, the reactor is substantially free of baffles suchas guide plates, agitators and the like. Inside the reactor, however,one or more feed pipes, for supplying reactants, may be mounted. Thesetypes of feed pipes may terminate at any point in the reactor, but theypreferably terminate in the region of the stream of bubbles beingproduced when the reactor is in the operating state, above the gasinjection device or in the vicinity of the surface of the liquid, butwithin the liquid.

Circulation is encouraged by the tapering lower section and furthermore,in the case of suspensions, suspension cut-off is produced andclassification of the solids particles takes place. The reactorpreferably consists of a cylindrical upper section and a conicallydesigned lower section, wherein the conical lower section, in accordancewith a preferred embodiment of the process, has dimensions such that itaccommodates at least half the volume of liquid to be circulated. Thereactor may also be rectangular and have a cuboid upper section and awedge-shaped, i.e. tapering to a point, lower section. The includedangle of the cone or lower section tapering to a point is generallybetween 45° and 150°, in particular between 60° and 120°. A port isarranged in the conical or wedge-shaped lower section for withdrawing asolids-rich suspension.

Thus, with reference to the accompanying drawings, FIG. 1 shows anascending jet reactor (1) which represents a preferred embodiment of adevice for performing the process according to the invention. Thecontainer comprises a cylindrical upper section (2) and a conical lowersection (3). The container lid contains a port (4) for extracting vaporsand for connecting to a vacuum system (not shown). A port (5) isarranged in the wall of the cone, for withdrawing a suspension. Theposition of this port is expediently below that of the suspensioncut-off established in the operating state. A device for gas injection(6), for example a perforated plate, is arranged at the tip of the cone.The gas is supplied through a port (7) and passes through the device forgas injection into the reactor. The reactor is substantially free ofbaffles. In the embodiment in accordance with FIG. 1, there is only onepipe (8) inside the reactor, this being used to introduce the liquidfeedstock and having its discharge opening (9) located in the region ofthe stream of bubbles produced in the operating state. In the operatingstate, i.e. when gas is being forced in or, preferably, when gas isbeing abstracted under reduced pressure, an extensive circulation flowis produced in the solution or suspension (10) found in the reactor, thedirection of flow being indicated by arrows.

In the embodiment in FIG. 2, a tubular device (26) for gas injection islocated at the tip of the conical lower section (23). The gas emergesfrom the annular gap formed by this device and an inlet pipe (28) whichis located centrally within this. The discharge opening (29) of theinlet pipe can be altered by shifting the pipe (28) so that the positionof the suspension cut-off, in processes in which suspended particles areinvolved, can be altered.

The process according to the invention is particularly suitable forprocesses during which a product is crystallized out of the liquidmedium or during which particles which increase in size are produced insome other way, for example by polymerization. Examples of applicationsof the process are the preparation of active oxygen compounds, forinstance H₂O₂ reaction products from the group consisting of sodiumpercarbonate, sodium perborate tetrahydrate, persulphates, alsoincluding the triple salt 2KHSO₅ KHSO₄ K₂SO₄, form amidine sulphinicacid. During in-situ preparation and crystallization, both an aqueousH₂O₂ solution and also the other reaction partner required, that issoda, sodium metaborate, Caro's acid and KOH or thiourea respectively,each being in a dissolved form and separate from the H₂O₂ or alreadymixed with it, are added to the reactor filled with mother liquor.Suspension is simultaneously withdrawn. After separating the crystalsfrom the suspension, one or more reaction partners is added to themother liquor which is then recycled in this form. The process is alsoextremely suitable for crystallizing amino acids.

It is assumed that three hydraulically separated regions are formed inthe ascending jet reactor, the effect of each on crystallization beinginterpreted as follows:

(i) Ascending region in the stream of bubbles: The reactants areintroduced here, with the advantage that axial bundling of the lines offlow maintains supersaturation of the solution and the heat of reactionand of crystallization is rapidly dissipated by vacuum cooling at thesurface. It has proven especially advantageous if the reactants areintroduced at as low a level as possible, that is just above thesuspension cut-off being formed, so that the supersaturated solutionencounters a high suspension density of preferably coarser particles.

(ii) Descending region in the outer parts of the reactor: As a result ofextensive circulation, transverse flow classification takes place. Fineparticles are drawn into the upper region in the stream of bubbles,while particles which are increasing in size migrate, on increasinglylonger paths, towards the tip of the tapering, preferably conical orwedge-shaped, lower section of the reactor.

(iii) Cut-off for the suspension density in the tapering (conical) lowersection: The diminution in the ascending stream occurring towards thetip of the cone restricts the hydraulic transport of particles. Thus, acut-off in suspension density is produced with increasing size andnumber of particles, at the same level as the hydraulic equilibrium.Thus, a highly concentrated, that is solids-rich, suspension can bewithdrawn at the base of the container, without sedimentation occurring.

As is well-known, secondary crystal seed formation is one of the mostimportant factors determining the particle size distribution of acrystallizate. Whereas, in the case of previously disclosed processesusing crystallizers containing a variety of different shapes of bafflesand agitators and/or pumps as circulation devices, improving poorparticle number regulation has been attempted by using chemicals and/orcomplicated equipment, the process according to the inventiondemonstrates unexpected advantages during a crystallization process:

Simple reactor, substantially without any baffles;

Simple control of circulation;

No break-down of particles due to rotating units or

deflections at sharp baffle edges;

Simple adjustment of residence time in order to produce a specific rangeof particle sizes;

Adjustable classification; No additional apparatus or process stepsrequired to isolate and redissolve fine particles.

One particular, totally unexpected advantage of the process according tothe invention is the modified foam producing behavior. Systems whichgenerally have a strong tendency to foam can be handled in the processaccording to the invention without any antifoam additives and alsomechanical devices for breaking down the foam are rendered superfluous.It is assumed that several effects contribute to this modifiedfoam-producing behavior:

(i) Depending on the gas injection conditions (pressure, size ofnozzles, temperature), it is quite possible to obtain large primarybubbles which burst during foam production. Gas injection is preferablyperformed using a nozzle with large nozzle openings (diameter in the 1to 10 mm range) and under reduced pressure (suction). (ii) Due to thepresence of the stream of rising bubbles, a large additional surfacearea is produced for evaporation, no vapor bubbles being produced duringthis process. (iii) Boiling bubbles, which are produced on theparticles, can diffuse during ascending jet circulation into theinterior of the gas bubbles very deep down in the reactor and so nolonger contribute, as large bubbles, to foam production, or do so to amuch smaller extent. High shear forces occur in the stream of bubblesand these cause the loosening of tiny bubbles. (iv) The very largestream of liquid circulating in the reactor is diverted at the surfaceand moves suddenly from the core flow to the outer region of thereactor, so that mechanical foam break-down and/or inhibition of foamproduction takes place during the nascent phase.

The device according to the invention is distinguished by a particularlysimple type of construction while at the same time providing highefficiency both with regard to reducing the tendency to form a foam ordestroying foam and also with regard to classifying particles suspendedin the liquid medium. In addition, virtually no incrustation problemsarise, due to the absence of baffles, apart from one or more inletpipes.

The following examples and comparison examples explain the invention.

COMPARISON EXAMPLE 1 Preparation of Sodium Percarbonate

a) Batchwise Crystallization

The crystallization reactor, designed as a vacuum container, was made ofglass and had a dished boiler head. Circulation was achieved using anagitator. The crystallization time was 60 min, the temperature was 15°C. and the pressure was 16 mbar abs.

A synthetic mother liquor comprising 45 kg of water, 10 kg of NaCl, 2.23kg of soda, 1.18 l of H₂O₂ (70 wt.%), 10 g of NaHMP (sodiumhexametaphosphate) and 50 ml of waterglass was initially introduced.

5.03 kg of soda and 30 g of NaHMP were added to the mother liquor(=made-up mother liquor). 2.92 l of an aqueous H₂O₂ solution (70 wt. %)were metered in.

Test 1: Using the synthetic mother liquor; the mother liquor with addedsoda was filtered before adding H₂O₂. After crystallization, sodiumpercarbonate was separated from the mother liquor and dried. Its activeoxygen content (Oa) was 13.9%, the proportion of fines (<0.2 mm) was 2%.

Test 2: Using the filtered mother liquor from test 1; the made-up motherliquor was filtered. The analytical data showed: Oa=14.4%, fines (<0.2mm)=14%.

Test 3: Using the synthetic mother liquor; the madeup mother liquor, incontrast to test 1, was not filtered. The analytical data showed:Oa=14.4%, fines (<0.2 mm) 14%.

Test 4: Using a non-filtered mother liquor from test 3, made-up motherliquor not filtered. The analytical data showed: Oa=14.4%, fines (<0.2mm)=24%.

In tests 1 to 4, in the absence of an antifoam agent, a deep layer offoam was produced. In addition, the proportion of fines was always veryhigh.

b) Continuous Crystallization

The crystallization reactor was the same as that in tests 1 to 4, but itwas provided with devices for the continuous addition of made-up motherliquor and H₂O₂ solution and also for continuous removal of thesuspension. A synthetic mother liquor with the same composition and inthe same amount as in comparison example 1 was initially introduced.After making up this solution with 5.03 kg of soda and 30 g of NaHMP,aqueous 70 wt. % strength H₂O₂ solution (molar ratio soda to H₂O₂=1:1.5)was metered in at 15° C., at a pressure of 16 mbar abs, over the courseof 1 hour and with stirring.

Test 5: Sodium percarbonate which had crystallized out was removed fromthe suspension discharged during crystallization; the mother liquorobtained in this way was made up, while retaining the ratio of motherliquor to soda and NaHMP, and filtered before being returned to thecrystallizer. The Oa content of the sodium percarbonate was 14.4%, thefines (<0.2 mm) amounted to 9%.

Test 6: if the made-up mother liquor was returned to the crystallizerwithout being filtered, the fines increased to 20 to 40%.

Intense foam production took place during continuous crystallization andan antifoam agent had to be added in order to maintain the vacuumrequired. Tri-n-butyl phosphate proved to be the best antifoam agent,this being added in an amount of 0.2 ml per liter of suspension in tests5 and 6.

Example 1 Preparation of Sodium Percarbonate

Continuous crystallization in vacuum in a crystallizer made of glasswith a cone in the lower section of the crystallizer. Circulation wasachieved using air injection. The air was introduced at the tip of thecone. In the lower part of the wall of the cone was a port for thewithdrawal of suspension. Aqueous H₂O₂ solution (60 wt. % strength) andmother liquor made-up with soda and NaHMP were metered in continuouslywith the molar ratio H₂O₂ to soda of 1.5. The inlet pipes terminatedbelow the surface of the liquid. Injection air: 365 Nl/h; averageresidence time about 1 h, temperature 25° C., pressure 44 mbar abs.,metering of made-up mother liquor: 14.7 kg/h (composition: 9.94 kg ofwater, 2.3 kg of NaCl, 2.38 kg of soda, 14.9 g of NaHMP, 40 ml of waterglass).

Test 1: The mother liquor was made-up after filtration (Nutsche) andmetered into the crystallizer without being filtered. After recyclingthe entire amount of mother liquor five times, the materials data forthe sodium percarbonate was: Oa=14.36%, fines (<0.2 mm)=1.9%, Dp₅₀=1.35mm.

Test 2: The mother liquor was made up without being filtered and meteredinto the crystallizer without being filtered. After recycling the motherliquor five times the materials data for the sodium percarbonate was:Oa=14.25%, fines (<0.2 mm)=0.6%, Dp₅₀=1.23 mm.

No foam problems occurred during continuous crystallization trials inaccordance with the principle according to the invention. Anapproximately 10 cm deep layer of foam remained stable during the tests.An antifoam agent was not added. The product is characterized by a lowproportion of fines.

Example 2 Preparation of Formamidine Sulphinic Acid (FSA)

Continuous crystallization under vacuum in a crystallizer made of glasswith a conically shaped lower section to the crystallizer. Circulationwas achieved using air injection—introduced from below at the tip of thecone. Inlet pipes and withdrawal ports in accordance with example 1.Injection air: 40 Nl/h, residence time about 2.5 h, temperature 6.5° C.,pressure 10 mbar abs.

Saturated FSA solution at 20° C. was initially introduced; thioureasolution (35 wt. %, 55° C.) was metered into the crystallizer; anaqueous H₂O₂ solution (35 wt. %) was also metered in, such that themolar ratio of H₂O₂ to thiourea was 2.01.

The FSA isolated from the withdrawn suspension had the followingmaterials characteristics: Dp₅₀=0.23 mm, FSA content=98.7%, TUcontent=<0.1%.

The amount of foam remained constant during continuous crystallizationand the amount did not increase as compared with the small amount offoam produced at the start.

Example 3 Crystallization of Thiourea (TU)

Continuous crystallization under vacuum in a crystallizer made of glasswith a cone in the lower section of the crystallizer (crystallizer inaccordance with examples 1 and 2). The inlet pipe for TU solutionterminated below the surface of the liquid in the region of the gentlestream of bubbles. A port for withdrawing solids-rich suspension waslocated in the lower part of the wall of the cone. Circulation wasachieved by air injection in an amount of 60 Nl/h. Residence time about1.8 hours, temperature 26.5° C., pressure 40 mbar abs. Initialfeedstock: saturated TU solution at 20° C., about 12 kg; thioureasolution (35 wt. %, 70° C.) was metered into the crystallizer,unfiltered, in an amount of 7.5 kg/h.

Thiourea with an average particle size of Dp₅₀=0.43 mm was obtained.Differently from conventional crystallization, surprisingly, there wasno foam production and nor were incrustations produced on the wall ofthe crystallizer.

Further variations and modifications of the foregoing will be apparentto those skilled in the art and are intended to be encompassed by theclaims appended hereto.

German priority application 196 50 959.9 is relied on and incorporatedherein by reference.

We claim:
 1. An ascending jet reactor comprising: a container for aliquid medium, and a device for gas injection in a lower, taperingsection of said container in a position which enables ascending jetcirculation and introduces a stream of bubbles into said container,wherein said reactor contains a port for withdrawal of a solids-richsuspension in the lower, tapering section and at least one inlet pipewith a discharge opening for introducing a liquid medium into thecontainer above the device for gas injection and extending into thecontainer, wherein the opening of the device for gas injection ispositioned at the bottom of the lower tapering section of the container,wherein the discharge opening of the inlet pipe is located inside theregion of said stream of bubbles produced while the reactor is underoperation, and wherein the container of the reactor is substantiallyfree of baffles.
 2. An ascending jet reactor according to claim 1,further comprising a port for connecting to a vacuum system.
 3. Anascending jet reactor according to claim 1, wherein the container forthe liquid medium comprises a cylindrical upper section.
 4. An ascendingjet reactor comprising: a container for a liquid medium, with a lowertapering sections substantially free of baffles, a device for gasinjection in said lower tapering section which enables ascending jetcirculation in the container, wherein the opening of the device for gasinjection is positioned at the bottom of the lower tapering section ofthe container, a port in the lower tapering section for withdrawal of asolids-rich suspension, at least one inlet pipe with a discharge openingfor introducing said liquid medium into the container, above the devicefor gas injection, and extending into the container, wherein thedischarge opening of the inlet pipe is located inside the region of astream of bubbles produced while the reactor is under operation, and aport for connecting to a vacuum system.
 5. An ascending jet reactoraccording to claim 4, wherein the container for the liquid mediumcomprises a cylindrical upper section.